Starter motors for heavy vehicles such as large trucks face a particularly onerous task in generating sufficient torque to turn over a large engine. For example, a truck engine of, say, 11 to 13 liter capacity, requires a starter motor producing at least 7 kilowatts of output power. Such a starter motor may draw an in-rush current of somewhere in the region of 1,300 to 2,200 Amps for a short period. This large starting current, occurring within typical vehicle wiring configurations, presents a number of problems which lead to poor starter performance and reliability, and consequential vehicle downtime. Some of the problems include:
A. Poor Starter reliability—Low starter output power and less than expected crank speed, contributing to longer than intended crank durations. This results in progressive damage to the starter motor commutator and associated components due to low voltage/high resistance within the earth connection which is not capable of efficiently conducting in-rush current in applications where more than 4 kW of output power is required.
B. Inadequate/Multiple points of termination for earth/ground connections. The terminal length of the single connection earth termination on existing starter motors cannot facilitate the total number of cables connections, including to the chassis, battery, engine and cabin earthing/ground cables. If the length of the single existing terminal were extended, the excessive leverage would exceed the load carrying capability of the commutator cover and thru bolts of the motor assembly being at a single connection/exit point.
C. Engine component and radiator damage as a result of high stray currents existing exceeding 500 mv peak to peak in the engine block (such that electrolysis erodes material away) causing leakage and/or ingress of fluid/chemical/water to sensors, especially in applications where engine coolant systems are not maintained properly.
D. Also, as noted in item C above, stray currents result in electrolysis, leading to erosion or accelerated corrosion of soft metals in the cabin and chassis, especially where dissimilar metals mate surface to surface.
E. Noise—Radio interference caused by ground loops in communication equipment fitted to a vehicle, as a result of poor earthing at multiple ground points, leading to illusive faults being logged by engine, gear box/transmission and body control modules.
There have been a number of attempts in the past to address one or more of these problems but, to date, none of them have really been successful. Each individual equipment manufacturer has worked to achieve compliance to industry standards and best engineering practices using different methodologies. Many utilise the chassis for earthing/grounding, such that the main chassis rail of the vehicle is utilised for earth, then multiple connections are made to it at various connecting points.
The above problems impact upon the starter motor manufacturer, the engine supplier and the truck builder. Each of these participants has significant commercial and reputational interests at stake. Each party, consciously or otherwise, attempts to shift responsibility for the problem and the cost burden of rectification and re-engineering onto other parties. Consequently, attempts at solving the problems have failed, due to lack of true collaboration and knowledge sharing. The present applicant, through its unique position in the supply chain, has been able to navigate between the parties and bring a holistic solution to the problem based on an understanding of starter motor technology, electrical engineering and application demands.
With the foregoing in mind, the present invention seeks to address one or more of the above problems.
Any discussion of documents, devices, acts or knowledge in this specification is included to explain the context of the invention. It should not be taken as an admission that any of the material formed part of the prior art base or the common general knowledge in the relevant art in Australia or any other country on or before the priority date of the claims herein.